1. Field of the Invention
This invention concerns the collection of machining cutting fluid liquid and chips from a number of machine tools to be filtered in a filtration system.
2. Description of the Prior Art
Industrial filtration equipment is often employed to filter cutting fluid liquid directed over the cutting tools during the machining process. The liquid, metal chips, and other debris generated are collected and circulated to filtration equipment for removal of the chips, with the filtered liquid returned to the system for reuse. This liquid collection has in the past been accomplished by return flow in so-called velocity trenches, which are below grade steel-lined concrete trenches equipped with jets of liquid spaced along the trench which direct the collected cutting fluid liquid, chips, and other debris along the trench and back to the filtration equipment. In a variation of this method used recently, a large volume of liquid is introduced at the beginning of the trench sufficient to carry the chips down the trench.
In recent years, below grade steel-lined trenches have become disfavored, since undetected leaks may occur through cracks in the trench, sometimes causing considerable contamination of the soil beneath the plant by the oil in the cutting fluid liquids. It is very difficult to find and repair such leaks, even if double-walled linings and leak detectors are used.
Copending U. S. application Ser. No. 08/131,298 filed on Oct. 8, 1993 by the present inventor, now U. S. Pat. No. 5,380,446, describes a vacuum collection system using in-line filter units. This approach requires pressurized filters, which are not currently in widespread use in this field. Rather, open-topped tank filters are typically employed.
Above grade piping networks have also been used, in which a pump is associated with each sump, pumping the collected liquid back to conventional filtration equipment via overhead pipes.
There are several disadvantages to this approach.
Firstly, having an industrial pump at each sump requires the wiring of each pump and starter with higher voltage lines. There are typically a large number of sumps involved with a typical installation, and thus involving substantial costs, particularly if a spare pump is specified for each sump so that the system need never be shut down for maintenance.
The extra pump at each sump increases the size of the sump, and also makes it impractical to collect liquid beneath each wing base in a transfer line as the pumps cannot be fit beneath the base.
The individual relatively small capacity pumps are not as durable as large capacity industrial pumps, creating a maintenance burden, particularly since these small capacity pumps, with their relatively tight clearances tend to become clogged with the machining chips.
U. S. Pat. No. 4,325,663 issued on Apr. 20, 1982 for an "ARRANGEMENT FOR CLEANING CUTTING FLUID," describes a vacuum collection system for sump cutting fluid only, with the chips and other heavy solids settled out and collected separately. This greatly complicates the collection and disposal of these solids, as there are numerous locations at which the chips are accumulated.
The sumps must have both cutting fluid liquid and machining chips removed and using relatively small pumps with correspondingly lower suction action has often necessitated cleanout of the sumps, creating a regular, ongoing maintenance burden.